Scanning lens antenna

ABSTRACT

An improved microwave antenna for use in aircraft guidance in which respective azimuth and elevation antenna are fed through dielectric lenses by respective rotating scanners to result in scanned planar beams without physical antenna rotation. The respective scanners are mechanically coupled to thereby insure synchronization so that radiation is fed to only one antenna at a time.

Minted States Patent 1191 1111 3,852,762 Henf et al. Dec. 3, T974 4]SCANNING LENS ANTENNA 2.524292 10/1950 1111113 et al. 343/76! 2,669,6572 1954 C tl 343 783 [75] Inventors: George Henf, Pleasantvllle; Leonard272L263 011955 g I I I 3432M Schwartz, Scarsdaleboth of 3,018,450 1 1962Hollis 333/9 A ig 'Ih Si g C p y, Falls Goodman r 1 NJ.

Primary E.\aminerEli Lieberman [22] Flled: 142 1973 Attorney, Agent, orFirmT. W. Kennedy [21] Appl. No.: 415,634

[57] ABSTRACT [52 us. 01 343/756, 343/761, 343/779, An improvedmicrowave antenna for use in aircraft 343 7 0 343 73 3 3 7 guidance inwhich respective azimuth and elevation 51 Int. (:1. H0lq 19/12, HOlq19/08 antenna are fed through dielectric 199898 y respective [58] Fieldof Search 343/757, 761, 839, 854, rotating Scanners to result in Scannedplanar beams 343 75 779 7 0 7 7 without physical antenna rotation. Therespective scanners are mechanically coupled to thereby insure 5References Cited synchronization so that radiation is fed to only onean- UNITED STATES PATENTS a 2,442,951 6/1948 lams 343/754 13 laims, 23Drawing Figures PLANAR AZIMUTH OUTPUT AZl MUTH REFLECTOR ELEVATIONFOLDED PILLBOX ELEVATION ROTATING FEED 6| AZlMUTH LINE FEED APERTUREAZIMUTH FOLDED PILLBOX AZIMUTH ROTATING FEED SCANNER PLANAR ELEVATIONOUTPUT ELEVATION OUTPUT HORN & POLARIZER lOl PATENIEQBEB 31914 (852,762

SHEET 10F 9 ROTATI N G STATIONARY DHEZGCTORS DIRECTOR 34 M ITE REDH-FLANE lll h? 11 36 ,1

xsn "lllllllllullml y SPLITTING LINE *1 i 36 F/ G. 2 l

OUTPUT PATENTELUEC 31974 SHEET 3 BF 9 m D R WD %ET 4 A 6E7 USN P EE4 CAOG A H OHR O FPF THIN FIBERGLASS PARALLEL-PLATE J WAVEGUIDE (AIR FILLED)THIN SHEET METAL LIGHTWEIGHT FOAM F/G. 5B

R E N N, A C 5 PAIENIEL 3mm SHEET 0F 9 OFF AXIS SCAN 2 ON AXIS SCAN mmm3M4 3,852,762

' sum 5 [IF 9 TANGENT C CENTER OF CIRCULAR RE FLECTOR F POINT AT WHICHFEED IS LOCATED R T TANGENT R /EI ED PIXTENTEL i 31914 -3;e52.7s2

SHEET 8 BF 9 79 COPPER SQUARES 78 COPPER STRIPS DOUBLY CURVEDELECTRONICS PARALLEL PLATE F EED MOUNTING STAND PATENTEL B 31974$852,762

sum 7 nr 9 CIRCULAR REFLECTOR FEED LENS 89 PARALLEL PLATE FEED SCANNERF/G. //A

8| SHAPED y K95 CIRCULAR REFLECTOR PARALLEL PLATE FEED 93 FEED LENSASSEMBLY SCANNER 85 F/G. //B

PLANAR 93 AZIMUTH OUTPUT AZIMUTH AZIMUTH REFLECTOR LINE FEED APERTUREAZIMUTH FOLDED PILLBOX AZIMUTH /ROTAT|N G FEED LSOANNER' PLANARELEVATION ELEVATION FOLDED OUTPUT PILLBOX ELEVATION ROTATING FEED 6|ELEVATION OUTPUT HORN & POLARIZER lOl SHEET 9 OF 9 TERMINATION /\|I5AZIMUTH SECTION OF scANNER AZIMUTH ANTENNA TION s LATOR F s NNER PORTI hI ELEVATION I III ANTENNA RF FR RF SOUR LOW LEvEL REFLECTED RF AZIMUTHSEC N TERMINATION 85 OF SCANNE AZIMUTH H3 f S I ANTENNA f PORT4 I PORT 3(I25 A I27"\, Q CI ENcOOER CIRCU- ELEvATION SECTION LATOR OF NNER PORT IPORT 2 U1 I EvATION I III TENNA RF FROM SCURCE RF LOW LEVEL REFLECTED RFSCANNING LENS ANTENNA BACKGROUND OF THE INVENTION This invention relatesto aircraft guidance in general and in particular to a unique antennamechanization which is capable of generating radar guidance signals ofthe proper character suitable for landing various types of aircraft,i.e., conventional fixed wing, short take off and landing (STOL) andhelicopter.

With the increase in air traffic, the need to expand instrumentedairports, and the variety and types of aircraft to be accommodated, thesingle approach profile provided by conventional UHF-VHF InstrumentLanding Systems (lLS) in use today is not adequate. To satisfy thespectrum of potential airborne users and the increasing variety ofairport ground facilities, a new type of scanning beam landing system isrequired. A variety of requirements and signal formats have beenidentified for various applications. Much .of this data has beensummarized in the documentation of the Radio Technical Committee forAeronautics subcommittee 1 l7. DO-l48 published by RTCA in November 1970is typical of this data.

Scanning beam landing systems have for the most part employed antennaswherein the entire antenna was physically rotated or nutated to provide,within the approach airspace, the scanning beam spatial motion necessaryfor landing guidance. This technique, i.e., total antenna motion, hasbeen primarily utilized since it does provide, the most straight-forwardmeans of minimizing any variations to the radiated radar beam pattern asit scans the approach airspace. This type of scanning antennamechanization does however have numerous limitations associatedwith it.Key limitations are:

A. The antenna structural supports needed to maintain stable operationin a rotational condition coupled with the high torque mechanical drivesubsystems necessary to start-up and rotate the entire antenna result inbulky heavy ground station equipments.

B. Since the entire volume swept by the scanning antenna must beenclosed to protect the antennas, the ground equipments are generallylarge.

C. When an antenna is scanned, the time period during which receivedguidance information is available to the approaching aircraft is notcontinuous. Furthermore, as the number of antenna scans per unit time isincreased, the received data (dwell time) per scan is correspondinglyreduced.

D. To provide the necessary lateral and vertical landing guidance datadictates that the scanning beams be swept in two orthogonal directions.To provide orthogonal antenna scan requires two antennas resulting inadditional ground station volume to accommodate each and additionalelectronic equipment to insure that these radiated beams sequentiallyscan the approach volume in order not to contaminate the received datee.g., beam synchronization.

In summary, the key requirements associated with the generation of scanbeam data for a scanning beam aircraft landing system are to:

1. provide orthogonal beam scan in the vertical and horizontal planes ofthe approach volume;

2. generate fan beam scanning data where the beam parameters areinvarient throughout the approach volume. This requirement can besimplified as follows: provide planar beam scan;

3. synchronize the scan of the individual beams (vertical andhorizontal) to avoid contamination of the received data that would occurif both were received simultaneously; and

4. generate beam data relatively free from distortions that may becaused by terrain elements in proximity to the ground station. That is,generate narrow main beam radiation and low level extraneous beamradiation (sidelobes).

SUMMARY OF THE INVENTION The objective of scanning lensantenna-microwave (SLAM) of the present invention is to satisfy theabove requirements and eliminate the aforementioned difficulties. TheSLAM mechanization generates narrow fan beams which scan orthogonallyusing a single lightweight, fixed antenna and circular lens scantechnique.

The unique features that can be realized from this technique are:

l. SLAM produces narrow fan beam scanning from a stationary antennaeliminating the need for rugged structure and large enclosuresassociated with non-stationary antennas;

2. the SLAM produces two orthogonal beam scans from a single flat plateconfiguration reducing dramatically the enclosure requirements;

3. the SLAM provides automatic self-synchronized scanning operationwithout requiring electronic switches, mechanical linkages, orelectronic circuitry; and

4. the SLAM permits scan rate of the actual beam in space to beindependent of the rotational speed of the internal lens-feed scanner byusing multiple feed lens assemblies.

The SLAM consists of an azimuth and elevation antenna each of which usesmultiple rotating feeds to generate the planar beam patterns requiredfor landing system applications. The elevation section of the SLAMantenna consists of a rotary scanner which has one fixed input portwhich sequentially couples to continuously rotating output ports.Connected to the rotating output ports are waveguide fed, dielectriclenses. The scanner lens configuration is so arranged that the excitedlens illuminates a folded pill box type microwave antenna which uses acylindrical reflector-180 bend. Thelens reflector combination results ina collimated microwave beam which rotates with the movement of the feedsystem. The output of the pillbox is a vertical circular horn which isused to output the planar scanning elevation beam.

The azimuth section of the integral antenna employs a rotary scannersimilar to the elevation section. Each output of the rotating section ofthe azimuth scanner is connected to a waveguide fed lens. The lenses,which are coupled to the scanner, rotate inside of a parallel platetransmission line. Lens energy directed from the rotary scanner is fedinto a bend. The output of the bent parallel plate transmission line isa circular horn which excites a doubly curved reflector. Thisfeedreflector system produces a planar azimuth beam whose elevationpattern is determined by the reflector cross section. As the lensrotates, the planar azimuth beam scans the approach volume. The azimuthand elevation rotary scanner are combined into a single mechanical unitand as such both output sections (A2 and El) rotate together. The twoantenna sections are electronically isolated so that each antennaspattern performance is completely independent of the other.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective viewillustrating the nature of a planar beam scan.

FIG. 2 is a plan view partially in cross section illustrating therotating scanner of the present invention.

FIGS. 3a 3d are schematic illustrations of the operation of the scannerof FIG. 2.

FIG. 4 is a perspective view of a pillbox antenna used in the presentinvention.

FIGS. 50 and 5b illustrate details of the antenna of FIG. 4.

FIG. 5c illustrates the relationship between the pillbox antenna and thescanner.

FIGS. 6a and 6b are schematic diagrams illustrating the manner in whichthe dielectric lens of the present invention collimates radiation.

FIG. 7a is a plan view illustrating the dielectric lens of the presentinvention.

FIG. 7b is an elevation view in cross section of the lens of the presentinvention.

FIG. 8 is a diagram illustrating the directions of the rays of radiationin the antenna of the present invention.

FIGS. 9a and 9b are respectively cross sectional and plan views of apolarizing arrangement used in the present invention.

FIG. 10 is a perspective view of the azimuth antenna of the presentinvention.

FIG. 11a is a plan view and FIG. 11b an elevation view illustrating thearrangement of the components within the antenna of FIG. 10.

FIG. 12 is a perspective view partially cut away illustrating thecombined azimuth and elevation antennas.

FIG. 13 is a schematic view illustrating the manner in which radiationis fed to the elevation antenna.

FIG. 14 is a similar view illustrating the manner in which radiation isfed to the azimuth antenna.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A key requirement forlanding system antennas is that they generate a fan beam shape as shownin FIG. 1. A fan or planar beam is a broadside or flat beam which isformed when the direction of radiation is perpendicular to the radiatingaperture. In planar beam scanning, the radiation pattern in the scanplane is a broadside beam with no change in the beam shape. In typicalfeed scan types of beam scanning, the phase front and peak directiondeviate from the normal to the radiating aperture as the array isscanned, producing a beam which has a conical shape, where the degree ofconing is a function of the scan angle. To achieve planar scanningrequires a unique antenna configuration.

The beam of FIG. 1 illustrates the elevation scan. A similar beam mustalso be generated in the azimuth direction, i.e., it would be rotated 90from the beam shown on the Figure. In the landing system the beams arescanned in sequence. That is, first an elevation scan is performed andthen an azimuth scan and then another elevation scan and so on.

ELEVATION ANTENNA The elevation antenna comprises a four output scanningdevice with four wave guide feeds and lens assemblies, a folded pillboxand a polarization rotator. The scanner has one wave guide input andfour outputs. each of which are terminated with a feed and dielectriclens assembly. There are no wave guide transitions (i.e., one linear tocircular transition and one circular to linear transition as required inthe rotating joint). The scanner arrangement is shown in FIG. 2. Thisdevice is based on the field theory of standard rectangular wave guidesoperating in the TEIO mode. For this mode the current density at thecenter of the two broad walls will be zero. This means that the waveguide can be split in half without affecting the propagationcharacteristics of the wave guide, by cutting it along the longitudinalcenter line. In such a split wave guide the upper half can be shiftedwith respect to the lower half along the longitudinal axis withoutaffecting the propagation characteristics of the waveguide.

As illustrated by FIG. 2, the rectangular wave guide which has sides 30and 31, is formed into an annulus in the H plane. The dividing linebetween the halves of the wave guide is the circle 32. In this way theouter half 33, having the wall 30, can be rotated with respect to theinner half 35, having the wall 31 without affecting the RF fields insidethe wave guide. In this particular application, the inner half 35 servesas a stator and the outer half 33 as a rotor. Energy is coupled into thescanner via a mitered H-plane bend 34. As shown on the figure, the miterextends halfway across the wave guide. In this application, the mitereddevice is called a director. The director has a length along the waveguide and, in this region the wave guide is below cutoff because thewide dimension is significantly smaller than half a free spacewavelength. Four similar directors 36 are placed in the rotor 33 atintervals so that the energy is coupled from the scanner by only onedirector at a time, since the other directors are separated from theactive one by a section of cutoff waveguides. Isolation is furtherenhanced by extending the input director 37 around the complete annulusexcept for the region corresponding to the desired scan sector.

Scanner operation is illustrated by FIG. 3. As shown thereon, when anoutput director is located opposite the input director, a short ispresented at the input and the incident energy is reflected in thedirection of the transmitter. The series of diagrams presented on FIG. 3shows the various positions of the rotor 33 with respect to the stator35. In FIG. 3a, the relative positions of the upper and lower halves ofthe waveguide are such that energy is coupled from the input tooutput 1. Outputs 2, 3, and 4 are isolated from the input due to thecutoff properties of the directors 36 and 37. In b, the upper half ofthe waveguide has been displaced with respect to the lower half suchthat shorting of the input waveguide is achieved. In c, the director 36afor output 4 is overlaying the input and the input waveguide is shorted.The input remains in the shorted condition until the direction 36a is inthe position shown in a. The dimension d is approximately half afreespace wavelength. In this position energy is now coupled from theinput to output 4.

Higher-order modes are excited within the waveguide in the region of thedirectors. These higher-order modes excite currents at the centerline 32of the waveguide wall that could result in a small level of energy beingleaked from the split in the waveguide. Standard, half-wave, foldedchokes are located at the Separation between the rotor 33 and stator 35on both the upper and lower sides of the waveguide. These chokes arecontinuous around the full waveguide annulus and create an electricalshort at the dividing line and these prevent any leakage of RF energyfrom the waveguide.

The diameter of the waveguide annulus is selected such that the timeperiods during which energy is coupled to an output and during which theinput is shorted, are consistent with the elevation radiation intervals.

The rotating scanner is a waveguide device and is capable of handling,without breakdown, power levels approaching that of a straight sectionof waveguide. The device also has a frequency bandwidth capacity ofgreater than percent. The VSWR over the band of frequencies from 15.4 to15.7 is less than 1.05:1 and the insertion loss is less than 0.5 dB.

FIG. 4 illustrates a typical pillbox antenna 40 which is found in theprior art.

The pillbox antenna illustrated is a parallel plate microwave system inwhich the radiation is confined to two dimensions between conductingsheets Hand 43 and a conducting backwall 45 acts as a reflectorcollimating the microwave energy. In a simple pillbox such as this thefeed system 47 is in the path of the radiated collimated energy from thereflector. This results in feed blockage and pattern deterioration. Toavoid this blockage a folded pillbox is used. Folded pillboxes have beendescribed in the literature such as the article by W. Rotman entitledWide Angle Scanning with Double Layer Pillboxes Trans IEEE PGAP Jan.1958.

The folded pillbox used in the present devices and shown on FIG. 5 usestwo sets of parallel plates, one indicated as set 49 containing theincident field from the feed and the other thereflected-collimated-field from the reflector. Each set of parallelplates forms a transmission line. The sections are connected by a 180bend 53 whose back wall forms a circular reflector in the elevationplane.

FIG. 5 also shows some details of the relative location of the scannerwith respect to the waveguide. The scanner 55 is placed within theplates 49 and rotated therein by the drive motor 57 in the mannerdescribed above. As can be seen more clearly from FIG. 5c, as thescanner 57 rotates each of the output ports in succession will directtheir energy toward the circular reflector of the 180 bend 53 to the setof plates 51 and directed out of the antenna aperture 59.

To minimize the tolerance requirements and reduce the production costsof the parallel plate pillbox spacing, a TEM propagation mode is excitedby the waveguide feed. This mode has its electric field perpendicular tothe plates. The wavelength for the TEM mode is independent of the platespacing and the tolerance is based on impedance mismatch considerations.Propagation of other modes is prevented by holding the plate separationto a dimension less than half a free space wavelength.

Small variations in the separation of the plates are not critical aslong as this half-wavelength maximum dimension is not exceeded. Since asandwich type of construction is utilized, and since the pillboxsurfaces are planar, the parallel plate spacing need not be maintainedto better than .020 inch throughout the structure for an operatingfrequency of l5.5GI- Iz.

The use of a TEM mode in the pillbox results in a horizontally polarizedradiation field which requires a polarization rotator to change thehorizontal polarization in the parallel plate line to a verticallypolarized radiating field. Y

Both a parabolic and circular reflector can be used with the pillboxantenna of FIG. 5. The circular reflector is preferred due to itssuperior off axis scanning properties. FIG. 6a shows that if theparabolic reflector is fed from its point focus, an in phase conditionoccurs at a plane AZ which is perpendicular to the reflector axis;However, as the feed is scanned off the point focus, the plane AZ tiltsbut an on focus condition no longer exists on it. This manifests itselfin unacceptable sidelobe levels, beam-broadening due to coma andnon-planar beam shape (conical). On the other hand a properly fedcircular reflector, as shown in FIG. 6b, will overcome this conditionsince the center of rotation for the feed and reflector are the samepoint. Thus the physical relationship between the two, remain constantas a function of rotation. At every feed angular position during. thescan, the same broadside aperture is obtained. This constantillumination with scan motion results in a scan pattern having a planarbeam shape with constant beamwidth and side lobes.

In order to feed a circular reflector it is necessary to use a lens tocompensate for its inherent spherical abberation. This is illustrated byFIG. 8 which shows that the reflected rays of a circular reflector areuncollimated if it is fed from a point source. To overcome this problem,a dielectrically loaded, parallel plate feed lens is used on the outputof each of the scanner feed horns. The lens is shaped such that itrefracts the rays so that they strike the reflector at an angle whichwill allow them to be reflected parallel to the antenna axis. The shapeof this lens is determined by applying two conditions upon the raysemitted from the lens:

I. that they be reflected off the reflector parallel to the antennaaxis; and

2. that in a plane perpendicular to the antenna axis, the rays all havethe same electrical path length. If these two conditions are satisfied,energy radiated from the reflector will be collimated in a plane wave ofuniform phase which provides a radiation pattern with a 2 halfpowerbeamwidth. Since the centers of rotation of the scanner and reflectorare coincident, the relative configuration of the antenna is invariantas a function of rotation and ture planar-beam scanning is achieved.FIG. 6b shows that if the feed lens 61 is moved along the arc AB notonly do the rays remain collimated but the beam is always perpendicularto generating source which in this case is the circular reflector. Thisis extremely important if planar beam shapes are to be maintained.

A typical feed lens 61 is shown on FIG. '7. Energy will be provided outof each of the outputs 1, 2, 3, and 4 of FIGS. 2 and 3 through awaveguide 63 to a lens 61. This lens 61 will comprise a parallel platedielectrically loaded feed lens. The dielectric material 65 is containedbetween two plates 67 and 69. The input end of the lens has a taperedmatching section 71. Once the dielectric constant of the lens medium andthe position of the feed horn required to obtain the required outputaperture size is determined, a lens shape may. be found thatsatisfiesthe condition noted above. For example, at 15 GHz, a 2 3DBelevation antenna, the reflector would be a cylinder with the radius ofcurvature of 20.9

inches. The point of the lens closest to the reflector is located at aradius of inches. The lens thickness is 0.261 inches, less than half afree space wavelength, to prevent higher order mode propagation and therelative dielectric constant of the lens material 1.50.

Since the energy in the folded-pillbox design is propagated in the TEMmode the polarization of the radiated energy is linear in the horizontaldirection. However, if vertically polarized energy is required, apolarization rotator can be placed across the aperture to providevertical linear polarization.

Several techniques for accomplishing the polarization rotation arepossible. These include a double array of parallel strips, an array oftwisted waveguides, and a double array of printed-circuit inductive andcapacitive elements. Any of these methods are suitable for the SLAMantenna. All but the technique incorporating twisted waveguides involveconversion of polarization from horizontal linear to circular and fromcircular to vertical linear. The first two techniques, arrays ofparallel metal strips and a combination of parallel metal and dielectricstrips, are both quite heavy and difficult to manufacture. In addition,it is necessary to adequately support the individual strips since theirorientation must be carefully maintained under shock and vibrationconditions. The method involving the twisted waveguide is astraightforward conversion technique. However, it is difficult tomanufacture and even heavier than the first two methods.

The fourth method of conversion provides a very lightweight,reproducible, structurally-sound unit. Such an arrangement is shown onFIGS. 9a and b. The device consists of six layers 75 of metal circuitsphotoetched on thin fibreglass sheets. A quarter-wave-thick sheet ofvery low density polyester foam 77 separates each of the fibreglasssheets.

The printed circuits consist of inductive and capacitive shuntsusceptance elements such as copper squares 79 and strips 78 arranged,as shown on FIG. 9b, so that an incident linearly polarized signal issplit into two orthogonal components and the phase of one element isdelayed with respect to the other. The first, third, fourth and sixthsheets are of the same design and the second and fifth sheets are thesame. The combination of the first three sheets divides the incidentlinearlypolarized energy. The combination of the remaining three sheetsprovides the reverse of this operation because of a 90 physical rotationof the three sheets. In this way the circularly-polarized energy isconverted to vertical linear, the desired orientation.

Polarization convertors of this type have been used in manyapplications. The mismatch of these devices is very small, less thanl.l:l, and the insertion loss is less than 0.5 dB. Frequency bandwidthsin excess of 10 percent are readily attained with this approach.

AZIMUTH ANTENNA The azimuth antenna shown on FIG. 10 utilizes the samescanner as the elevation antenna with similar lens but does not requirethe folded pillbox. In this case the lenses rotating about a scanneraxis 80 feed a section of parallel plate transmission line 81 which isused as the feed for a doubly curved reflector 83 which is the antennaradiating aperture.

As in the case of the elevation antenna the radiating aperture must becurved, in the scan plane, to maintain the planar beam shape. Thereflector and the feed both have a circular shape in the azimuth planewhose center of rotation is coincident with the scanner center ofrotation as shown on FIG. 11A.

As shown thereon, there is a scanner 85 such as that described above,with one waveguide 87 shown terminating in a lens 89. The lens will bewithin the parallel plate feed 81 shown on FIG. 10 which terminates in acircular shape as indicated by the circle 91. Energy is then radiated tothe circular reflector 93.

In order to keep the structure compact, a right angle bend 95, shown onFIG. 11B, is included in the parallel plate feed 81. In the elevationplane the reflector 93 is shaped so as to generate a csc 0 pattern whichminimizes the energy on the ground while increasing the signal levelabove the beam peak.

The actual reflector shape is designed using an existing computerprogram which provides an analytic solution based on geometric optics.This method of calculation has been described in the literature by A. S.Dun bar, "Calculation of Double Curved Reflector for Shaped Beams," Oct.1948. Proceedings of the IRE- Wave And Electron Section, and consists oftransforming the feed radiation into the described reflector radiationpattern using geometric optics equations.

Side lobe control is maintained in a number of ways. In the elevationplane the actual radiation pattern of the parallel plate feed is used tocalculate the reflectors shape by the above mentioned method. In theazimuth plane the scanner output feed and lens are carefully designedand constructed in order to maintain the proper phase and amplitudedistribution on the reflecting surface. Finally in the parallel platefeed itself, extreme care is used to insure a homogeneous transmissionpath so that minimum phase and amplitude distortions are introduced.

COMBINED ELEVATlON/AZIMUTH ANTENNA The elevation and azimuth antenna arecombined in a single synchronized unit as illustrated by the cutawayperspective view of FIG. 12. Reference numerals used in the descriptionof FIG. 12 will be the same as those previously used where possible toaid in collating the previously described figures with FIG. 12. Twoscanners, both the elevations scanner and the azimuth scanner will belocated on a common axis in the direction of arrow 98. The elevationantenna is located in the front, with its scanner 55 feeding its fourlens 61, one of which is shown, which then direct the energy to thefolded pillbox 99 from which it is directed through a right angle bendto the elevation output horn and polarizer 101. The resulting elevationscan is illustrated by the energy patterns 103 shown as being emittedfrom the horn 101. The azimuth scanner is not shown. However, one of itslenses 89 can be seen which directs the energy through its foldedpillbox 81 to the reflector 93 as described above. The azimuth radiationpattern is illustrated by the beams 105 from the reflector 93. To keepthe antenna unit as compact as possible, two right angle bends,respectively, bend 107 and bend 109, have been added to the elevationantennas folded pillbox resulting in the elevation beam being radiatedout normal to the plane of the scanner. Each antenna section providesthe required planar beam throughout its scan sector. The scanners forthe two antennas may be machined as a common unit and driven by a singlemotor. Angular position information is provided by a sin gle, directlydriven encoder. Synchronization of the azimuth and elevation beams isensured by the inherent design of the switching section. It is unique inthat the normal power consuming active RF switch has been replaced witha passive ferrite circulator. The circulator in conjunction with theantenna scanner not only accomplishes the switching function butpresents a constant impedance to the RF source. The switching functionitself relies on the properties of the ferrite circulator and theantenna scanner. This portion of the operation is illustrated on FIGS.13 and 14. RF energy is developed in conventional manner from an RFsource and is provided into the system on a waveguide 111. From thewaveguide 111 it enters a ferrite circulator indicated generally as 113.The circulator 113 contains four ports labelled ports 1 to 4. Radiationenters through port 1. A conventional termination 115 is coupled to port4. Port 2 is coupledto the elevation scanner and port 3 to the azimuthscanner via waveguides 117 and 119 respectively. On the drawing, asindicated by'the key, RF energy is a heavy solid arrow and low levelreflected energy by dashed arrows.

The scanner sequentially couples each antenna to the appropriateterminals of the circulator. The combination of circulator/scannerautomatically-directs the RF energy to the first available activeantenna. The nature of the scanner is such that either the azimuth orthe elevation antenna is capable of receiving this RF energy. Thescanner never permits both antennas to get RF energy simultaneously.Note that both the elevation section 55 and azimuth section 85 of thescanner have four radiating elements, represented by the light areas121, spaced 90 apart. The shaded areas 123 separating these elementsrepresents that portion of the scan when a short circuit is presentedatthe antenna terminals. The relative positions of the elevation andazimuth segments is fixed when the single scanner is fabricated.

On FIG. 13, the scan cycle has been stopped with the azimuth portion 85of the scanner in a short circuit condition and the elevation portion ina radiating condition. RF energy from the RF source enters Port 1 of thecirculator 113, rotates around the first circulator junction 125 in acounterclockwise direction to the second circulator junction 127 whereit is rotated counterclockwise to Port 2. At Port 2 it sees theelevation antenna, through the open scanner 55 and is radiated. Any lowlevel energy reflected by the elevation antenna ia reflected back intothe circulator and rotated to Port 3 where the azimuth portion 85 of thescanner is short circuited. it is once again reflected back into thecirculator 113 and rotated to Port 4 where it exits to the RFtermination 115.

FIG. 14 shows the scanner advanced to the azimuth radiate position andthe elevation portion of the I scanner short circuited.

Azimuth RF energy enters the circulator 113 at Port 1, is rotated toPort 2 where it encounters the short circuited elevation portion 55 ofthe scanner and is reflected back into the circulator. Here it isrotated to Port 3 and passes through the open azimuth antenna. Anyenergy reflected by the radiating antenna is reflected back into thecirculator 113 and rotated to and exits from Port 4 to the RFterminator.

When properly indexed, a single encoder 125 coupled to the shaft 127driving the scanners provides antenna positional information for theentire azimuth/elevation scan cycle. During the interval when neitherelevation nor azimuth information is required the scanner automaticallypresents a short circuit to the RF source which causes the RF to bereflected back through the circulator 113 and into the termination 115thereby automatically isolating the RF source from the antenna.

As described above, a circular feed aperture into the parallel plateswas disclosed which resulted in a planar output scan. lt is alsopossible to obtain a conical scan with the antenna of the presentinvention by providing a linear feed aperture into the parallel plates.

Thus, an improved scanning lens antenna which provides a planar beamoutput useful in landing system applications has been shown. Although aspecific embodiment has been illustrated'and described, it will beobvious to those skilled in the art that various modifications may bemade without departing from thespirit of the invention which is intendedto be limited solely by the appended claims.

What is claimed is:

1. A scanning lens microwave antenna comprising:

a. a fixed circular reflector;

b. a scanner comprising an annular shaped rectangular waveguide split inhalf with the inner half containing a fixed inlet port and forming astator and the outer half containing a plurality of rotatable outletports and forming the rotor and means in said waveguide to cause onlyone output at a time to couple to said input;

0. a parallel plate waveguide directing energy from said scanner to saidreflector whereby said scanner will scan energy across said reflector;and

d. a parallel plate dielectric lens located at the end of said parallelplate waveguide, said dielectric lens mounted within a thin metal outercasing which is coupled to said waveguide and having a tapered matchingsection extending into said waveguide.

2. The invention according to claim 1, wherein said means to couple oneoutput at a time comprises a stationary director in the stator having amitered H-plane extending partially across the input port and aplurality of rotating directors in said rotor one being provided foreach output port and having a mitered l-l-plane bend extending partiallyacross its associated output port.

3. The invention according to claim 2, wherein said stationary directoris extended around the major portion-of said stator.

4. The invention according to claim 2, wherein said parallel plate waveguide comprises a pillbox antenna with the end of said pillbox providingsaid curved reflector.

5. The invention according to claim 4 and further including apolarization rotator at the output of said pillbox antenna.

6. The invention according to claim 5, wherein said pillbox hasadditional parallel plate bends and terminates in an output horn whichis perpendicular to the plane of the scanning lens within said pillbox.

7. The invention according to claim 5, wherein said polarization rotorcomprises a plurality of printed circuits comprising a pattern in copperon thin fiber glass and a plurality of low density foam dielectricspacers of a thickness of one quarter wave length sandwiched betweensaid plurality of printed circuit boards.

8. The invention according to claim 2, wherein said curved reflector isa doubly curved surface having a circular shape in the direction ofscanning.

9. The invention according to claim 8, wherein said parallel platescontain bend of essentially 90 to direct energy to said curvedreflector.

10. The invention according to claim 9, wherein said parallel plateshave a circular feed aperture to produce a planar output scan.

11. The invention according to claim 9, wherein said parallel plateshave a linear feed aperture to produce a conical scan.

12. A scanning lens antenna for providing alternate orthagonally scannedbeams comprising:

a. a first scanning lens antenna comprising:

l. a pillbox antenna having its end formed to provide a curvedreflector;

2. a rotatable scanner including means to direct energy toward saidcurved reflector within said pillbox; and

3. a first parallel plate dielectric lens interposed between saiddirecting means and said reflector to cause the reflected energy to becollimated as it leaves said curved surface;

b. a second scanning lens antenna having its scanner mechanicallycoupled to the scanner of said first scanning lens antenna such thatonly one of said first and second lens antennae is able to radiate atone time, said scanning lens comprising:

l. a double curved reflector having a circular shape in the direction ofscanning; 2. a rotatable scanner including means to direct energy towardsaid double curved reflector; 3. a parallel plate wave guide enclosingsaid scanner; and 4. a second parallel plate dielectric lens interposedbetween said directing means and said reflector to cause the reflectedenergy to be collimated as it leaves said curved surface; c. means tosupply microwave energy to said first and second lens antennae; and (1.means to rotate the scanners of said first and second lens antennae. 13.The invention according to claim 12, wherein said means to supplymicrowave energy comprises:

a. an RF source;

b. a first three port ferite circulator having one port coupled to saidsource and a second opposite port coupled to a terminator;

c. a second ferite circulator having one port coupled to the input ofsaid first scanning lens antenna, a second opposite port coupled to saidsecond scan ning lens antenna and a third port coupled to the third portof said first circulator.

1. A scanning lens microwave antenna comprising: a. a fixed circularreflector; b. a scanner comprising an annular shaped rectangularwaveguide split in half with the inner half containing a fixed inletport and forming a stator and the outer half containing a plurality ofrotatable outlet ports and forming the rotor and means in said waveguideto cause only one output at a time to couple to said input; c. aparallel plate waveguide directing energy from said scanner to saidreflector whereby said scanner will scan energy across said reflector;and d. a parallel plate dielectric lens located at the end of saidparallel plate waveguide, said dielectric lens mounted within a thinmetal outer casing which is coupled to said waveguide and having atapered matching section extending into said waveguide.
 2. The inventionaccording to claim 1, wherein said means to couple one output at a timecomprises a stationary director in the stator having a mitered H-planeextending partially across the input port and a plurality of rotatingdirectors in said rotor one being provided for each output port andhaving a mitered H-plane bend extending partially across its associatedoutput port.
 2. a rotatable scanner including means to direct energytoward said curved reflector within said pillbox; and
 2. a rotatablescanner including means to direct energy toward said double curvedreflector;
 3. a parallel plate wave guide enclosing said scanner; and 3.a first parallel plate dielectric lens interposed between said directingmeans and said reflector to cause the reflected energy to be collimatedas it leaves said curved surface; b. a second scanning lens antennahaving its scanner mechanically coupled to the scanner of said firstscanning lens antenna such that only one of said first and second lensantennae is able to radiate at one time, said scanning lens comprising:3. The invention according to claim 2, wherein said stationary directoris extended around the major portion of said stator.
 4. The inventionaccording to claim 2, wherein said parallel plate wave guide comprises apillbox antenna with the end of said pillbox providing said curvedreflector.
 4. a second parallel plate dielectric lens interposed betweensaid directing means and said reflector to cause the reflected energy tobe collimated as it leaves said curved surface; c. means to supplymicrowave energy to said first and second lens antennae; and d. means torotate the scanners of said first and second lens antennae.
 5. Theinvention according to claim 4 and further including a polarizationrotator at the output of said pillbox antenna.
 6. The inventionaccording to claim 5, wherein said pillbox has additional parallel platebends and terminates in an output horn which is perpendicular to theplane of the scanning lens within said pillbox.
 7. The inventionaccording to claim 5, wherein said polarization rotor comprises aplurality of printed circuits comprising a pattern in copper on thinfiber glass and a plurality of low density foam dielectric spacers of athickness of one quarter wave length sandwiched between said pluralityof printed circuit boards.
 8. The invention according to claim 2,wherein said curved reflector is a doubly curved surface having acircular shape in the direction of scanning.
 9. The invention accordingto claim 8, wherein said parallel plates contain bend of essentially 90*to direct energy to said curved reflector.
 10. The invention accordingto claim 9, wherein said parallel plates have a circular feed apertureto produce a planar output scan.
 11. The invention according to claim 9,wherein said parallel plates have a linear feed aperture to produce aconical scan.
 12. A scanning lens antenna for providing alternateorthagonally scanned beams comprising: a. a first scanning lens antennacomprising:
 13. The invention according to claim 12, wherein said meansto supply microwave energy comprises: a. an RF source; b. a first threeport ferite circulator having one port coupled to said source and asecond opposite port coupled to a terminator; c. a second feritecirculator having one port coupled to the input of said first scanninglens antenna, a second opposite port coupled to said second scanninglens antenna and a third port coupled to the third port of said firstcirculator.